1. Field of the Invention
The present invention relates to an electromagnetic-type fuel injection valve used in an internal combustion engine, and more particularly to a fuel injection valve which can reduce operating sound and can enhance the fuel metering performance by making use of a squeezing reaction force of a liquid (residual fuel) occurring in the periphery of a movable core at the time of closing the valve.
2. Description of the Prior Art
An electromagnetic-type fuel injection valve used in an internal combustion engine is generally constituted such that a fuel connection tube is fixedly secured to an upper portion of a body, an electromagnetic solenoid is disposed in the inside of the body, a movable core which is slidably movable by an excitation of the electromagnetic solenoid is provided, a needle valve is mounted on a distal end side of the movable core, a nozzle body which is provided with a valve seat is mounted on a distal end side of the body in such a manner that the nozzle body surrounds the needle valve. And further, an insert tube is inserted into the inside of the fuel connecting tube, and a coil spring which biases the needle valve in a valve closing direction is disposed between the insert tube and the movable core.
As this type of fuel injection valve, a fuel injection valve having the following construction was previously proposed in Japanese Laid-Open Utility Model Publication 165965/1984. That is, a fixed core portion is provided at a distal end portion of a fuel connecting tube positioned in the inside of an electromagnetic solenoid. A movable core is disposed such that the movable core can be brought into contact with the distal end side of the fixed core portion. At the time of opening the valve upon actuation of the electromagnetic solenoid, the movable core which is integrally formed with a needle valve is electromagnetically attracted to the fixed core portion side so that a proximal end surface of the movable core portion is brought into contact with the distal end surface of the fixed core portion. At the time of closing the valve, the needle valve is slidably moved in a distal end side thereof due to a coil spring and also the fuel pressure, so that a valve element is brought into contact with a valve seat of a nozzle body, and so that the distal end surface of the movable core approaches an end surface of the nozzle body, thus closing the valve.
Although the fuel injection valve having such a structure gives rise to a gap between the distal end surface of the movable core and the end surface of the nozzle body at the time of closing the valve, since the gap is several hundred xcexcm, and hence is extremely wide, the valve element of the needle valve which closes the valve due to a biasing spring force of a coil spring and also the fuel pressure strongly impinges on the valve seat of the nozzle body at the time of closing the valve. Here, a large impact occurs, thus giving rise to a problem that operating sound of a high level occurs. Further, since the impact at the time of closing the needle valve is large, the valve element is xe2x80x9cbouncedxe2x80x9d at the time of closing the valve as a result of the impact. Hence, the valve is still slightly opened after the closing of the valve, thus leading to an unintended secondary injection due to this bouncing. Accordingly, there arises a problem that the metering performance of the fuel injection amount which can be accurately controlled based on the valve opening time is deteriorated.
It is an object of the present invention to provide a fuel injection valve which can reduce the operating sound at the time of closing a needle valve, and which can also prevent the deterioration of fuel metering performance which occurs as a result of bouncing of a valve element at the time of closing the valve.
The fuel injection valve of the present invention is constituted such that a needle valve and a movable core are movably disposed in an axial direction in the inside of a body which incorporates an electromagnetic solenoid therein, a fixed portion which the movable core approaches at the time of closing the valve is disposed in the body, and a gap is formed between the movable core and the fixed portion at the time of closing the valve. Here, when fuel remaining in the gap between the movable core and the fixed portion is pressurized corresponding to the movement of the movable core to the valve closing side, a squeezing portion is disposed at a portion which constitutes a passage for the fuel extruded from the gap.
It is effective if the size of the gap between the movable core and the fixed portion is set at 3.5 xcexcm-32 xcexcm.
Further, the squeezing portion which constitutes the passage for fuel extruded from the gap can be formed in the inside of a sleeve which is positioned at an outer periphery of the movable core.
Still further, the squeezing portion which constitutes the passage for fuel extruded from the gap can be formed by bulging an inner peripheral portion of a sleeve inwardly in a ring-like shape.
Further, an annular fixed member can be fixedly secured at a fixed position in the inside of the body as the fixed portion.
The fuel injection valve having the above-mentioned constitution is further provided with a nozzle body which is fitted into the distal end side of the body such that the nozzle body covers the needle valve from the outside, a valve seat formed around an injection opening provided at a distal end portion of the nozzle body, and a coil spring which biases the movable core to the distal end portion side.
Further, as another example, a nozzle body is fitted into the inside of the distal end of the body, an annular plate-like spacer is fitted between an inner peripheral shoulder portion of the body and a proximal end portion of the nozzle body, and a portion of the plate-like spacer which is protruded in the inside of the nozzle body is formed as the fixed portion.
Further, in the fuel injection valve which fixedly secures the annular fixed member at a given position in the inside of the body, a small-diameter portion may be formed on the distal end side of a movable core, and a squeezing portion may be provided at an inner peripheral portion of the annular fixed member which guides an outer peripheral portion of the small diameter portion.
Still further, in the above-mentioned fuel injection valve, by partially adding a plate-like space or a wedge space in a gap formed between the movable core and the fixed portion, the squeezing reaction force applied to the movable core at the time of closing the valve may be adjusted.
In the fuel injection valve having such a constitution, at the time of opening the valve, upon excitation of the electromagnetic solenoid, the movable core is electromagnetically attracted and retracted together with the needle valve toward the proximal end side, that is, the fixed core portion side which compresses the coil spring. Accordingly, the valve element provided at a distal end of the needle valve is separated a given distance from the valve seat so as to open the valve, and the fuel is injected from the injection opening of the valve seat.
On the other hand, at the time of closing the valve, the electric signal to the electromagnetic solenoid is cut off to stop the excitation thereof and hence, the movable core and the needle valve are moved toward the distal end side due to a biasing force of the coil spring and also the fuel pressure. Accordingly, the valve element provided at the distal end of the needle valve comes into contact with the valve seat so as to close the valve. At this point of time, that is, at the time of moving the movable core in the valve closing direction, that is, toward the fixed portion, the fuel which remains in the gap formed between the proximal end surface of the fixed portion and the distal end surface of the movable core is sandwiched and receives a pressing force. This fuel passes through the squeezing portion, and is discharged through the gap formed between the proximal end surface of the movable core and the distal end surface of the fixed portion.
Here, the movable core generates the squeezing reaction force (reaction force against the squeezing-out force or pushing-out force generated at the time of pressurizing the liquid and squeezing the liquid through the gap). Since the squeezing reaction force is increased in an inversely proportional manner to the cube of the size of the gap between the movable core and the fixed portion, even when the gap between the two surfaces which face in an opposed manner (that is, the gap between the proximal end surface of the fixed portion and the distal end surface of the movable core) is small, a large squeezing reaction force is generated. Also, a quick braking force is applied to the movable core and the needle valve due to this squeezing reaction force slightly before the point of time when the valve is closed. Accordingly, at the time of closing the valve, the impinging speed (seating speed) at a point of time that the valve element impinges (seats) on the valve seat is reduced or attenuated, so that operating sound at the time of closing the valve can be reduced. Further, by reducing the impinging speed of the valve element, the bouncing generated in the valve element at the time of impinging can be suppressed. As a result, the secondary injection after closing the valve can be minimized and hence, the metering performance of the fuel injection can be enhanced.